Other Parts Discussed in Thread: THVD1512, THVD1511, THVD1552
Hello,
I have designed a system that will eventually have 100+ nodes communicating at full duplex 115kbps using RS485.
In testing, I have discovered that using the THVD1551 as the full duplex RS485 transceiver, the nodes receive perfectly well regardless of how many are connected to the bus. However when more than one node is on the bus (in addition to the "primary" device), the ability of any individual node to transmit no longer functions correctly: the signal becomes significantly attenuated.
Re-re-reading section 9.4.2 Table 3 of the datasheet, I see that since the THVD1551 is always enabled as driver and receiver, the Y/Z pair are actively driven to H/L, respectively, when the node is idle. Therefore, my suspicion is that this is causing the signal problem: one node is idle, therefore driving the Y/Z pair to the H/L state, while the active node is trying to counteract those states during transmission.
Is this correct? If so, is there a solution to this so that multiple nodes can use the THVD1551 to drive the Y/Z pair? The datasheet doesn't indicate that the THVD1551 is inappropriate for use as a full duplex transceiver in a multiple node configuration.